Re: [PATCH 3/8] mikrobus: Add mikrobus driver
From: Ayush Singh
Date: Thu Sep 12 2024 - 09:33:12 EST
On 9/12/24 01:33, Greg Kroah-Hartman wrote:
On Wed, Sep 11, 2024 at 09:32:21PM +0530, Ayush Singh wrote:
On 9/11/24 20:27, Greg Kroah-Hartman wrote:
On Wed, Sep 11, 2024 at 07:57:20PM +0530, Ayush Singh wrote:
A simple platform driver for now that does nothing. This is required
because without a platform driver, the mikrobus_gpio0 nexus node cannot
be used.
In future, this driver will also allow for dynamic board detection using
1-wire eeprom in new mikrobus boards.
Signed-off-by: Ayush Singh <ayush@xxxxxxxxxxxxxxx>
---
MAINTAINERS | 1 +
drivers/misc/Kconfig | 17 +++++++++++++++++
drivers/misc/Makefile | 1 +
drivers/misc/mikrobus.rs | 32 ++++++++++++++++++++++++++++++++
4 files changed, 51 insertions(+)
diff --git a/MAINTAINERS b/MAINTAINERS
index 0cc27446b18a..d0c18bd7b558 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -15433,6 +15433,7 @@ MIKROBUS CONNECTOR
M: Ayush Singh <ayush@xxxxxxxxxxxxxxx>
S: Maintained
F: Documentation/devicetree/bindings/connector/mikrobus-connector.yaml
+F: drivers/misc/mikrobus.rs
MIKROTIK CRS3XX 98DX3236 BOARD SUPPORT
M: Luka Kovacic <luka.kovacic@xxxxxxxxxx>
diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
index 3fe7e2a9bd29..30defb522e98 100644
--- a/drivers/misc/Kconfig
+++ b/drivers/misc/Kconfig
@@ -610,6 +610,23 @@ config MARVELL_CN10K_DPI
To compile this driver as a module, choose M here: the module
will be called mrvl_cn10k_dpi.
+menuconfig MIKROBUS
+ tristate "Module for instantiating devices on mikroBUS ports"
+ help
+ This option enables the mikroBUS driver. mikroBUS is an add-on
+ board socket standard that offers maximum expandability with
+ the smallest number of pins. The mikroBUS driver instantiates
+ devices on a mikroBUS port described by identifying data present
+ in an add-on board resident EEPROM, more details on the mikroBUS
+ driver support and discussion can be found in this eLinux wiki :
+ elinux.org/Mikrobus
So you want to be a bus? Or just a single driver? I'm confused, what
exactly is this supposed to do?
If a bus, great, let's tie into the proper driver core bus code, don't
"open code" all of that, as that's just going to make things messier and
harder to work overall in the end.
If a single driver, why is it called "bus"? :)
thanks,
greg k-h
Well, mikroBUS [0] is the name of the socket standard. It is basically a
group of following pins:
Analog - AN
Reset - RST
SPI Chip Select - CS
SPI Clock - SCK
SPI Master Input Slave Output - MISO
SPI Master Output Slave Input - MOSI
VCC-3.3V power - +3.3V
Reference Ground - GND
PWM - PWM output
INT - Hardware Interrupt
RX - UART Receive
TX - UART Transmit
SCL - I2C Clock
SDA - I2C Data
+5V - VCC-5V power
GND - Reference Ground
I do not think it would qualify as as a "bus" in the Linux driver sense.
Especially with the devicetree based approach here which applies overlay
directly to the actual uart/i2c/spi controllers and basically not interact
with the mikroBUS node much.
It will be a "bus" in the driver sense as you want to have different
drivers bound to devices that are plugged in here, right? Or if this is
just a single driver for the hardware, then no, as you will not have any
additional drivers for this standard? It's unclear you want to do here.
No, a single driver. The driver is for board detection and applying
proper overlay. There will not be separate drivers for each addon board.
The driver is here to enable the following:
1. Enable dynamic board detection using 1-wire eeprom on some addon boards.
Some, not all?
Some mikroBUS boards have 1-wire eeprom [0]. This can be used to enable
dynamic detection of the board. But this is not part of mikroBUS
specification itself, and is like a mikroe addition. So there will be a
lot of mikrobus addon boards that do not have any way to do dynamic
detection.
2. Provide sysfs entry for runtime board adding/removal
That's not what sysfs is for, but we can get there eventually...
3. Enable using mikrobus connector node as nexus node for GPIO (not having a
platform driver makes any driver trying to use the connector as nexus node
go into deffered probing state).
Why is this a platform device? Is this always going to be described by
DT somehow?
Well, since greybus does not use a dt based approach right now, that is
one case where we potentially cannot describe the connector in DT. But
since greybus is mostly staging, I am not sure if there are any plans to
use DT before bringing it to mainline.
For this patch series, the driver is mostly here due to point 3. Basically a
stub.
Let's see how this really works before coming to conclusions.
As an example, how do you think sysfs should look for this device? For
all devices? Write out the needed sysfs documentation entries first and
then that will help explain things better.
thanks,
greg k-h
Something like the following:
cat board-overlay.dtbo > /sys/bus/platform/mikrobus-connector0/new_device
And to remove the device (revert the overlay)
echo 1 > /sys/bus/platform/mikrobus-connector0/delete_device
The main motivation for the sysfs entry is that only the board overlay
needs to be provided, since the driver already knows it's own connector
(and hence the symbols overlay for the connector).
[0]: https://github.com/MikroElektronika/click_id
Ayush Singh